In a conventional cellular communication system, multiple “macrocells” that each have a communication region with a radius of several hundred meters to several kilometers are formed and communication is executed. Since a communication region of each macrocell is large, the strength of a radio wave is low and the quality of communication is reduced in places such as a boundary region between macrocells, an indoor place, and a basement. Thus, recently, a “femto cell base station” (femto base station), a small base station that forms a “femto cell” with a radius of approximately 10 meters, has been installed in each of the places so as to inhibit a reduction in the quality of communication. Communication is executed using Wireless Fidelity (WiFi) in femto cells. Thus, the femto base station has a WiFi interface.
Recently, instead of 3G, Long Term Evolution (LTE) that enables a higher communication rate than 3G tends to be widely used as a communication scheme that enables communication terminals such as smartphones to be connected to each other in macrocells. Thus, it is expected that a femto base station that has an LTE interface will be installed in each of the aforementioned places in the future. It is, therefore, expected that if a communication terminal that has wireless interfaces for both LTE and WiFi is positioned in any of the aforementioned places, the communication terminal will be able to be connected to both LTE and WiFi simultaneously. In this case, the femto base station may improve the throughput of a certain traffic flow (hereinafter merely referred to as “flow” in some cases) by executing link aggregation (hereinafter referred to as “LA” in some cases) on the flow so as to communicate with the communication terminal using a communication link for LTE and a communication link for WiFi simultaneously. Especially, it is important that the throughput of a flow in the transmission control protocol (TCP) be improved for the LA. The TCP is used by many applications. Hereinafter, the communication link for LTE is referred to as an “LTE link” in some cases, and the communication link for WiFi is referred to as a “WiFi link” in some cases.
In the LA executed on a certain flow in the TCP, the femto base station uses a predetermined distribution algorithm for a flow in a “downlink” (hereinafter referred to as “DL” in some cases) directed from a server to the communication terminal so as to distribute data packets included in the DL flow to the LTE link and the WiFi link on a packet basis. In this case, the femto base station measures the utilization (for example, the utilization of a physical resource block (PRB) of the LTE link) of a wireless line and appropriately distributes the data packets at an appropriate time using the result of the measurement as a parameter to be input to the distribution algorithm, for example.